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ISO5452-Q1: Desat pin design value

Niya Tojo
Prodigy 20 points
Part Number: ISO5452-Q1

Tool/software:

We use Coolsic Mosfet which utilize SiC technology.To drive lower leg Mosfet we use gate driver with part no ISO5452-Q1 which have desat protection.We are designing desat protection with balnking capacitor of 47uF ,Rlim=5.1kOhm & Diode .Are these values ok for design?Will there be any Desat triggering issue if we use this value?

  • +1
    TI__Expert 5080 points

    Hello Niya, 

    Will the blanking capacitor be 47uF or 47pF? 47pF is a reasonable value (shown in your image), 47uF blanking capacitor would take too long to charge up to protect SiC effectively. 

    With a 5.1kOhm resistor and a HV diode in the path, the Vds detection threshold would be: 

    9V-5.1kOhm*500uA-Vdiode = 6.45V-Vdiode

    So as long as the diode drop voltage is within reasonable value (0.7V-2.5V), I would say the Vds protection threshold is reasonable. Of course this has to work for your system. 

    Thanks,

    Vivian

  • +1
    Prodigy 20 points

    Hello Vivian, thankyou for the answer. May i also know answer for following queries

    1)if 1pF is used instead of 47pF can the circuit still  work without unnecessary triggering of Desat?

    2)Will the circuit work properly if we use 11KOhm and 1pF?

    Mosfet which we are using is AIMDQ75R027M1H and Diode US1MHE3.

  • +1 in reply to Niya Tojo
    TI__Expert 5080 points

    Hi Niya, 

    1. ISO5x5x has a ~330ns deglitch on DESAT so that can help with false triggering. However a 1pF capacitor is usually too low, we usually see customer using caps in the tens-hundreds pF range. You can place a 47pF there and adjust it in testing if necessary. 

    2. 9V-11kOhm*500uA-Viode = 3.5V-Vdiode, which can possibly work. 1pF is a bit too low. Again, you can plan 11kOhm in initial schematic and change it later if DESAT false triggers during normal operation. 

    Vivian